Slab avalanche cycle in Rescue Creek

Location Name: Forecaster Observation - Rescue Creek, Flathead Range Observation date: Monday, February 18, 2019 - 15:15	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

Tabs

Quick Observation

We took advantage of today's clear weather to look for avalanche activity associated with last weeks storm cycle. We chose Rescue Creek in the Middle Fork for its plethora of steep avalanche terrain.

A widespread natural slab and loose dry avalanche cycle occurred in the Rescue Creek basin last week. The majority of slides observed were on steep south-facing slopes with several on north-facing terrain. Avalanches occurred both mid-storm and near the end of the storm.
A "very rough" guess of approximately 40-50 crowns noted with most appearing to be storm slab avalanches. The combination of crowns filled in with new snow, occasional low clouds and poor lighting prevented an accurate count.
At least two of the slides were particularly large (D3.5) with impressive debris piles up to 15' deep. We believe one of these was a Persistent Slab avalanche.

Snowpack, Avalanche, Weather Images:

Travel Details

Region:

Flathead Range - Middle Fork Corridor

Route Description:

Up Rescue Creek.

Activity:

Skiing

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

3500-5000 ft

5000-6500 ft

Aspect(s) of observation:

Persistent Weak Layers:

Facets or Faceted Crust

Buried

New Snow in the past 24 hours:

0.00in.

Total Snow Depth:

102"

More comments about the snowpack and weather:

Low-density surface snow was found at mid and upper elevations with the top 3-4" developing soft slab (F-) characteristics as we gained elevation. We did not travel into the upper elevations due to the numerous avalanches which we investigated. The recent north-east winds did not affect the areas we traveled in this drainage with the trees still heavily snow covered. At 4400' the snow depth is 102"!

Air temperature:

Below Freezing

Snow line:

Sky Cover:

Mostly Clear (FEW)

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Friday, February 15, 2019 - 18:15

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Within storm snow

More information or comments about the avalanche:

Extensive Storm Slab cycle during the loading event Friday and Saturday. It appears that some slides occurred earlier in the week as well. Crowns were noted on south, southeast, north, and northwest aspects.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

South

Starting Elevation:

5000'-7000'

Size

Destructive Size:

D2 Could bury, injure, or kill a person.

Relative Size:

R3 Medium

Crown Height:

1 ft

Avalanche Length (Vertical Run):

300ft.

Avalanche Width (Average width):

100ft.

Avalanche Location:

Date and Time of Avalanche:

Friday, February 15, 2019 - 23:30

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

The debris from these slides is noticeably larger than the numerous storm slab avalanches that occurred within the storm snow.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

South

Starting Elevation:

5500' - 7000'

Size

Destructive Size:

D2.5

Relative Size:

R3 Medium

Crown Height:

2 ft

Avalanche Length (Vertical Run):

1000ft.

Avalanche Width (Average width):

100ft.

Avalanche Location:

Date and Time of Avalanche:

Friday, February 15, 2019 - 23:30

Avalanche Type:

Unknown

Failure Plane/Weak Layer:

Old snow

More information or comments about the avalanche:

Could not identify the crown and therefore the size is an estimate and the avalanche-type is unknown. The debris traveled a long way on the valley floor (3/4+ mile) before coming to rest at 4500'. Numerous other paths fed this tongue of debris.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

Southeast

Starting Elevation:

above-treeline

Size

Destructive Size:

D3.5

Relative Size:

unknown

Crown Height:

2 ft

Avalanche Length (Vertical Run):

2000ft.

Avalanche Width (Average width):

300ft.

Avalanche Location:

Date and Time of Avalanche:

Saturday, February 16, 2019 - 06:30

Avalanche Type:

Hard Slab

Failure Plane/Weak Layer:

Old snow

More information or comments about the avalanche:

The crown height is an estimate of the maximum depth. This slide appears to have been triggered by a surface slide near the end of the storm and left an impressive debris pile.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

Northwest

Starting Elevation:

6600'

Size

Destructive Size:

D3.5

Relative Size:

R3 Medium

Crown Height:

5 ft

Avalanche Length (Vertical Run):

1000ft.

Avalanche Width (Average width):

400ft.

Avalanche Location:

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